Before the local gradients to the central server, the clients need to encrypt the plaintext of the gradients to prevent a malicious central server from learning private information from the gradients [1]}. We employ the state-of-the-art HE scheme CKKS (Cheon-Kim-Kim-Song) [2]} to encrypt each gradient. CKKS ensures both privacy and computability so that the gradients can be safely sent to the server for further processing.
